Anatomy and Physiology of the Bladder
The bladder is a sac-like organ in the pelvis that stores the urine produced by the kidneys.
There are two tubular structures called ureters (one from each kidney) that drain the urine
into the bladder. The urethra is the outflow tract of the bladder and connects the bladder
to the exterior.
- Click image to enlarge -
Anatomically, the bladder is the most anterior (closest to the front) organ in the pelvis, located just behind the
pelvic bone. Organs closest to the bladder include the rectum (the last part of
the colon), which is the most posterior (closest to the back) organ in the pelvis, the prostate gland and seminal
vesicles (in males), and the uterus, ovaries and fallopian tubes (in females). In males,
the prostate gland and seminal vesicles (organs that contribute secretions in semen) are
situated below the bladder and in front of the rectum. In females, the uterus (the womb),
ovaries and fallopian tubes are located posterior the bladder and anterior to the rectum.
The bladder itself is made up of four layers. These layers are important landmarks in
determining how deeply the tumor has invaded and the ultimate stage of the cancer.
- Epithelium: The epithelium, which lines the bladder and is in contact with the urine,
is referred as transitional epithelium or urothelium. Most bladder cancers originate from
the cells of this transitional epithelium. The urethra, ureters and the pelvis of the kidney
are also lined by this transitional epithelium, therefore, the same types of cancers seen in
the bladder can also occur in these sites.
- Lamina propria: Under the epithelium is the lamina propria, a layer of connective tissue
and blood vessels. Within the lamina propria, there is a thin and often discontinuous layer
of smooth muscle called the muscularis mucosae. This superficial layer of smooth muscle is
not to be confused with the true muscular layer of the bladder called the muscularis propria
or detrusor muscle.
- Muscularis propria or detrusor muscle: This deep muscle layer consists of thick smooth
muscle bundles that form the wall of the bladder. For purposes of staging bladder cancer, the
muscularis propria has been divided into a superficial (inner) half and a deep (outer) half.
- Perivesical soft tissue: This outermost layer consists of fat, fibrous tissue and blood vessels. When the tumor reaches this layer, it is considered out of the bladder.